Bicyclic .beta.-lactam antibiotics of the type represented by the above formula which have a four-membered .beta.-lactam ring fused to a six-membered oxazine ring have been described by Narisada et al., U.S. Pat. No. 4,138,486 and Belgium Pat. No. 863,998. For example, Narisada et al., described the 1-oxa-.beta.-lactam compound substituted in the 3-position of the oxazine ring with the 1-methyl-1H-tetrazol-5-ylthiomethyl group and in the 7-position with a phenylmalonamido group as represented by the following formula. ##STR3##
Because of the high antibacterial activity of this new type of .beta.-lactam antibiotic research workers have been stimulated to search for even more potent antibiotics of this bicyclic type.
The compounds of this invention, although related to the compounds described by Narisada et al., differ structurally by having a cyanomethyl substituted tetrazole moiety at the 3-position of the six-membered oxazine ring.